1. Field of the Invention
The field of the present invention relates to an electrical connector. More particularly, the field of the present invention relates to a totally shielded DIN connector.
2. The Prior Art
Electromagnetic interference or high frequency and radio frequency signals are often radiated or conducted to susceptible electronic equipment and interfere with the performance of that equipment. Electromagnetic interference sources includes sparks, lightning, radar, radio and TV transmission signals, brush motors and line transients. Sparks from a static discharge often are sources of electromagnetic Interference. By means of line conduction or by propagation through the air, electromagnetic interference may induce undesirable voltage signals in electronic equipment. Such interference is especially prevalent at connection devices such as in a DIN type connector.
In order to prevent electromagnetic interference from occurring at a connector and to keep a proper signal transmission from one or more devices utilizing the connector, two methods are commonly used. A first method utilizes a filter device coupling the connector's contacts in order to filter undesired signals from the circuit itself. The second method utilizes a metal shield to cover the outer surfaces of the connector for preventing external electromagnetic interference from penetrating into the insulator of the connector. The present device relates to the second method, that is an improved outer shielding of the connector for substantially eliminating the adverse effects of electromagnetic interference.
Conventional outer shielding for connectors involves two types of structures. A first group utilizes two separate shields, an inner shell and an outer shell, for coupling the connector. Examples of this type of connector include U.S. Pat. Nos. 4,637,669, 4,894,027, 4,913,664, 4,936,795, 4,938,714, 4,946,400, 5,017,158, 5,035,615. The first group of patents as exemplified in U.S. Pat. No. 4,637,669 fails to achieve an adequate shielding effect from electromagnetic interference. For example, the '669 patent lacks a front shield for protecting the contact accommodating apertures which make contact with another connector or device. Because the electromagnetic interference is especially prevalent and may concentrate at the point of connection, this type of shield is inadequate to provide the required shielding effect.
Another group of conventional connectors utilizes a one-piece shield and includes U.S. Pat. Nos. 4,842,554, 4,842,555, 4,908,335, 5,037,330. The present device provides an improvement over the latter group of connectors described in the aforementioned patents.
U.S. Pat. No. 4,842,554 ('554), discloses a one-piece shield covering four exterior sides of a DIN connector for providing shielding as well as grounding. The obvious disadvantage of this type of connector is that the back or rearward surface of the connector remains exposed to the propagation of electromagnetic interference through the air so that such a connector achieves an imperfect shielding effect.
What is desirable is a five sided shield which would be capable of shielding at least the front face, the top face, two side faces and the back face of a DIN connector. The bottom face of the connector from which the contacts of the connector extend outwardly in order to engage the corresponding apertures on a base such as a printed circuit board, for example, is typically left unshielded because good connection can be made with the base. Moreover, the base itself, such as a printed circuit board, also has a shielding effect.
However, it is difficult and uneconomical from a time and materials standpoint to form a five sided shell by stamping only a single piece of metal. The five sided shell when stretched flat prior to bending, typically forms an irregular outline. That is, it is not a simple matter to obtain a compact layout or arrangement of workpieces for stamping a sheet of metal to form a five sided shell. The process for stamping a five sided shell from a single flat sheet of metal often results in a waste of much of the original sheet of metal because the irregular shapes of metal resulting from the stamping process cannot be recovered for other uses.
In addition, a conventional connector such as that exemplified by the '554 patent is subject to constraints in the assembly process. In the '554 patent, the cantilever fingers extend in a horizontal direction. Thus, it is necessary to assemble the shield to the insulator from the front face. It is not possible for the type of one piece shield as shown in the '554 patent, to be combined with the insulator in any way other than from the front.
It will be appreciated that a conventional one piece shield cannot have five sides formed before assembly with an insulator. In such a case, it would be impossible to combine the shield and the insulator. For a one piece, five sided shield, the only direction from which the insulator can be inserted into the shield is from the bottom. Because the front face of the shield includes fingers which are extended rearward in a horizontal direction, the horizontally extending fingers will prevent the shield from simply being slipped over the insulator.
The rearwardly extending fingers require that the insulator be inserted into the shield from the backside. This is the only direction which would enable the fingers extending from the front face of the shield to be received within the annular recess of the insulator. However, in a conventional one piece, five sided shield, the rear wall would prevent the insulator from being combined with the shield from the back. Thus, a one piece shield such as shown in the '554 patent is incapable of being formed with five sides.
In addition, a conventional one piece shield cannot simply have a rear wall provided in a cantilever configuration prior to assembly, and then bent down to provide a five sided shield covering the rear face of the insulator. The additional step of bending the rear wall during the assembly of the shield to the insulator would unduly complicate the manufacturing process, could possibly damage the insulator and is economically infeasible.
Further, in the '554 patent, only a single piece of metal is used to form the four sided outer shell. The top wall of the shell is formed by bending an edge over the top of the insulator to engage the corresponding edges of the side wall in an edge to edge connection. A gap inevitably exists between the two opposite confronting edges and thus decreases the shielding effect. Other examples of spaces occurring between opposite confronting edges of the shield are shown in the '026 and '664 patents.
Another disadvantage of the conventional shell structure for shielding an electrical connector arises from the rough edges of the inwardly extending contact members. In the manufacturing process of a one piece four sided shield, the contact members extend inwardly from the front opening. These contact members are formed by a bending process so that it is usual to have sharp or rough edges along the inwardly extending contact members. Also, the rough edges of the front opening are exposed to the exterior. This makes the appearance look rough and is undesirable from a customer standpoint. This also causes a mating surface to have a sharp edge which may result in an imperfect connection with another component or in unintentional damage to other components when handling the connector assembly. Additional disadvantages of conventional DIN connectors relate to the need for grounding the connector to prevent the build up of parasitic capacitances and to shunt interfering electromagnetic signals to ground. In a conventional DIN connector, grounding is accomplished by the use of a grounding plate attached to the connector shield and having a connection with an additional grounding means such as a main ground lead for shunting interfering signals to ground as in the case of a computer. As shown in FIG. 1, in a conventional DIN connector 100, the ground plate must be fastened by a pair of screws 110 on the shield 120 and the insulator 130. This has the disadvantage of increasing the number of components for assembly and making assembly time consuming and piecemeal because assembly of the screws is not ordinarily integrated with other assembly steps.